1. Field of the Invention
The present invention relates to an image capturing apparatus and a control method thereof, and more particularly to auto-focus control technology in an image capturing apparatus.
2. Description of the Related Art
Conventionally, contrast AF methods are well known as a focus detection method used in the auto-focus detection apparatus of a camera. With a contrast AF method, the high frequency component is extracted from an image signal obtained using the image sensor, a contrast evaluation value indicating a focus state is derived from the high frequency component, and the position of the focus lens is controlled so that this contrast evaluation value is maximized.
In such a contrast AF method, the following problems exist when, in the case of deriving the contrast evaluation value of a predetermined focus control area in order to bring the focus control area into focus, luminance saturation occurs in the focus control area. That is, the peak of contrast evaluation values that ought to appear at the focus position is misshapen due to the influence of luminance saturation, and focus control accuracy deteriorates.
In view of this, a focus control detection apparatus that expands the focus control area in the case where luminance saturation continues to occur in the focus control area for longer than a prescribed period has been proposed (e.g., see Japanese Patent Laid-Open No. 10-213840). By performing such expansion control, the adverse influence caused by the peak of contrast evaluation values that ought to appear at the focus position being misshapen due to the influence of luminance saturation can be reduced.
In Japanese Patent Laid-Open No. 10-213840, expansion and focus detection are performed with respect to one focus control area, although in the case of performing focus detection with a plurality of focus control areas, a configuration can be adopted in which the focus control areas adjoin one another. With such a configuration, the focus control areas cannot be expanded, and the technique of the Japanese Patent Laid-Open No. 10-213840 cannot be used.